(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of forming a thermally stable cobalt silicide film in the fabrication of integrated circuits.
(2) Description of the Prior Art
Cobalt disilicide (CoSi2)is a preferred salicide technology as CMOS device sizes shrink to 0.18 xcexcm and beyond because of its good performance with small polysilicon and active area line widths. Cobalt disilicide also has been widely accepted in deep sub-micron devices to reduce the contact resistance. As device scales shrink further and molecular processes evolve, the requirement for cobalt disilicide film properties becomes more stringent. One of the concerns over the cobalt disilicide (CoSi2) film properties is its thermal stability. It is known that the thermal stability of CoSi2 is thickness dependent. That is, the thinner the CoSi2 film, the more thermally unstable it becomes. The sheet resistance of the thin CoSi2 film could be increased significantly when it experiences a thermal stress in subsequent processing. On the other hand, for shallow junctions, the CoSi2, thickness must be decreased. Thus, the CoSi2 film thermal stability for thin films must be improved.
A number of patents disclose methods of forming CoSi2. U.S. Pat. No. 6,022,457 to Huang et al discloses cleaning the native oxide layer off the silicon substrate, then depositing a titanium layer under the cobalt layer. A silicon layer may be deposited over the titanium layer and under the cobalt layer. A RTA process forms CoSi2. U.S. Pat. No. 6,083,817 to Nogami et al teaches a tungsten nitride capping layer over the cobalt layer. U.S. Pat. No. 6,025,267 to Pey et al discloses a titanium nitride layer over the cobalt. U.S. Pat. No. 5,869,396 to Pan et al shows a method of forming cobalt disilicide.
A principal object of the present invention is to provide an effective and very manufacturable method of fabricating a cobalt disilicide film in the fabrication of an integrated circuit.
A further object of the invention is to provide a method of fabricating a thermally stable cobalt disilicide film in the fabrication of an integrated circuit.
Yet another object is to provide a method of forming a thermally stable cobalt disilicide film by using a titanium stuffing technique.
In accordance with the objects of the invention a method for forming a thermally stable cobalt disilicide film in the fabrication of an integrated circuit is achieved. A semiconductor substrate is provided having silicon regions to be silicided. A cobalt layer is deposited overlying the silicon regions to be silicided. A capping layer is deposited overlying the cobalt layer. The substrate is subjected to a first rapid thermal anneal whereby the cobalt is transformed to cobalt monosilicide where it overlies the silicon regions and wherein the cobalt not overlying the silicon regions is unreacted. The unreacted cobalt layer and the capping layer are removed. A titanium layer is deposited overlying the cobalt monosilicide layer. Thereafter the substrate is subjected to a second rapid thermal anneal whereby the cobalt monosilicide is transformed to cobalt disilicide. During this transformation, some titanium atoms diffuse into and are incorporated into the cobalt disilicide film. The titanium layer is removed to complete formation of a thermally stable cobalt disilicide film in the manufacture of an integrated circuit.